title: Approach to knowledge of the interaction between the constituents of contact lenses and ocular tears: mixed monolayers of poly(methyl methacrylate) and dipalmitoyl phosphatidyl choline.
abstract: Mixed monolayers of poly(methyl methacrylate) (PMMA), the main component of hard contact lenses, and dipalmitoyl phosphatidyl choline (DPPC), a characteristic phospholipidic constituent of ocular tear films, were selected as an in vitro model in order to observe the behavior of contact lenses on the eye. Using Langmuir monolayer and Brewster angle microscopy (BAM) techniques, the interaction between both components was analyzed from the data of surface pressure-area isotherms, compressional modulus-surface pressure, and relative film thickness versus time elapsed from the beginning of compression, together with BAM images. Regardless of the surface pressure at which the molecular/monomer areas (A(m)) were recorded, the A(m) mole fractions of PMMA (X(PMMA)) plots show that the experimental results match the theoretical values calculated from additivity rule A(m) = X(PMMA)A(PMMA) + X(DPPC)A(DPPC). The application of the Crisp phase rule to the phase diagram of the PMMA-DPPC system can explain the existence of a mixed monolayer made up of miscible components with ideal behavior at surface pressures below 25 mN/m. However, at very high surface pressures, when collapse is reached (at 60 mN/m), the single collapsed components are segregated into two independent phases. These results allows us to argue that PMMA hard contact lenses in the eye do not alter the structural characteristics of the phospholipid (DPPC) in tears.
authors.affiliation: Department of Optometry, School of Optics and Optometry, University of Santiago de Compostela, Campus Sur. 15706-Santiago de Compostela, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Miñones Conde
authors.forename: O
authors.initials: O
authors.lastname: Conde
authors.forename: J M
authors.initials: JM
authors.lastname: Trillo
authors.forename: J
authors.initials: J
authors.lastname: Miñones
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D003261:Contact Lenses / Q000009:adverse effects*; D004347:Drug Interactions; D006801:Humans; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013666:Tears / Q000737:chemistry*
chemical_list: D015060:1,2-Dipalmitoylphosphatidylcholine; D019904:Polymethyl Methacrylate